Methods and systems for remote sleep monitoring

Abstract

Methods and systems for remote sleep monitoring are provided. Such methods and systems provide non-contact sleep monitoring via remote sensing or radar sensors. In this regard, when processing backscattered radar signals from a sleeping subject on a normal mattress, a breathing motion magnification effect is observed from mattress surface displacement due to human respiratory activity. This undesirable motion artifact causes existing approaches for accurate heart-rate estimation to fail. Embodiments of the present disclosure use a novel active motion suppression technique to deal with this problem by intelligently selecting a slow-time series from multiple ranges and examining a corresponding phase difference. This approach facilitates improved sleep monitoring, where one or more subjects can be remotely monitored during an evaluation period (which corresponds to an expected sleep cycle).

What is claimed is: 
     
       1. A method for remote sleep monitoring, the method comprising:
 transmitting a radar signal toward a subject; 
 receiving a radio frequency (RF) response signal corresponding to the radar signal; 
 monitoring vital signs of a subject, the vital signs comprising a respiratory signal and a cardiac signal, the monitoring of the vital signs comprising:
 processing the RF response signal, the processing comprising:
 producing vital sign signals, the vital sign signals comprising the respiratory signal and a mixed respiratory and cardiac spatial channel; 
 extracting the cardiac signal from the mixed respiratory and cardiac spatial channel; 
 producing spatio-temporal data of motion response in the RF response signal; and 
 range gating the spatio-temporal data to produce a plurality of spatial channels comprising one or more respiratory spatial channels and one or more mixed respiratory and cardiac spatial channels; and 
 monitoring the vital sign signals over an evaluation period; and 
 
 
 classifying a sleep state of the subject based on results from monitoring the vital signs. 
 
     
     
       2. The method of  claim 1 , wherein the radar signal is a radar impulse signal. 
     
     
       3. The method of  claim 2 , wherein the radar signal is an ultra-wide band (UWB) radar impulse signal. 
     
     
       4. The method of  claim 1 , further comprising determining whether the subject has a sleep disorder based on classifying the sleep state. 
     
     
       5. The method of  claim 1 , wherein processing the RF response signal further comprises applying a circle fitting algorithm to the plurality of spatial channels to correct for direct current (DC) offset. 
     
     
       6. The method of  claim 1 , wherein processing the RF response signal further comprises identifying the one or more mixed respiratory and cardiac spatial channels based on phase rotation of the plurality of spatial channels. 
     
     
       7. The method of  claim 6 , wherein identifying the one or more mixed respiratory and cardiac spatial channels comprises identifying spatial channels having an expected phase rotation arc. 
     
     
       8. The method of  claim 7 , wherein processing the RF response signal further comprises identifying the one or more respiratory spatial channels from spatial channels having a phase rotation arc outside the expected phase rotation arc. 
     
     
       9. The method of  claim 1 , wherein extracting the cardiac signal from the mixed respiratory and cardiac spatial channel comprises:
 extracting the respiratory signal from the one or more respiratory spatial channels; and 
 removing the respiratory signal from the one or more mixed respiratory and cardiac spatial channels. 
 
     
     
       10. The method of  claim 9 , wherein:
 the respiratory signal is extracted from a selected respiratory spatial channel of the one or more respiratory spatial channels; and 
 the respiratory signal is removed from a selected mixed respiratory and cardiac spatial channel of the one or more mixed respiratory and cardiac spatial channels. 
 
     
     
       11. The method of  claim 10 , wherein the selected respiratory spatial channel and the selected mixed respiratory and cardiac spatial channel are selected based on which combination among the one or more respiratory spatial channels and the one or more mixed respiratory and cardiac spatial channels produces a higher signal to noise ratio (SNR). 
     
     
       12. The method of  claim 1 , wherein the radar signal comprises ultra-wide band (UWB) radar impulses having a bandwidth between 1.0 gigahertz (GHz) and 2.0 GHz. 
     
     
       13. The method of  claim 1 , wherein the evaluation period comprises a predicted sleep cycle of the subject. 
     
     
       14. The method of  claim 1 , further comprising monitoring vital signs of multiple subjects over the evaluation period.